What is Metronidazole?

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  • Written By: Mary McMahon
  • Edited By: Kristen Osborne
  • Last Modified Date: 13 September 2019
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Metronidazole, known by a number of trade names including Flagyl, is an antibiotic medication useful for treatment of infections with anaerobic organisms such as some bacteria and protozoans. This medication is available by prescription only and can usually only be obtained after an examination, as doctors want to avoid prescribing it when a patient does not need it. A variety of formats are available including liquids, topical creams, and tablets designed for different applications, and this medication is also approved for veterinary use.

This drug works by targeting the DNA of anerobic organisms in the body. One advantage to using metronidazole is that it usually leaves aerobic organisms like beneficial gut fauna alone, and it also does not target human cells. This reduces harmful side effects. The drug also tends to have a soothing effect on the bowel and may be prescribed in the treatment of colitis and diarrhea.

Metronidazole is used in the treatment of a variety of conditions including bacterial vaginosis, abscess, protozoal infections of the gut, and Clostridium difficile infection. A doctor may want to take a sample for biopsy and culturing before prescribing the medication, or it may be offered on the basis of the symptoms the patient is experiencing. Preparations of metronidazole are sometimes used in dermatology to treat skin infections.


Patients on this medication can experience nausea and diarrhea, despite the fact that the medication has a protective effect on the bowel. Adverse reactions with alcohol are also a documented problem and it is advisable to avoid drinking while taking this medication and for several days after finishing a course of metronidazole. Some patients also develop more serious side effects like darkened stool or urine, headaches, and fatigue. Patients who experience harmful side effects should call their doctors for advice.

There is debate about the safety of metronidazole usage during pregnancy. Some members of the medical community feel the medication is beneficial and can in fact reduce the risks of going into early labor. Others fear the medication may have teratogenic effects because it is designed to target and damage DNA. Studies on the issue have been inconclusive and patients should talk to their obstetricians about the safety of using this medication during pregnancy, and should make sure their doctors are aware of a pregnancy when prescriptions are being written. This medication can also be dangerous for people with liver or kidney damage, as they may have difficulty metabolizing it.


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Post 2

@dfoster85 - Yuck! The thing about treating either yeast or BV is that either treatment can kill off your good bacteria, making it possible for bad stuff to grow. It's a good idea to always load up on probiotics (yogurt!) when you're treating any sort of vaginal infection.

Metronidazole is effective, but for either yeast or BV, there might be natural options. For BV, a study found that a hydrogen peroxide vaginal wash would be as effective as antibiotics. (I am not sure if it would be safe during pregnancy.) Another advantage of the hydrogen peroxide treatment is that it encourages the growth of good bacteria, to help restore the balance.

For yeast, natural treatments include vinegar, yogurt, and gentian violet.

Post 1

You can also get metronidazole as a gel; my doctor said that the gel might be better for women who are pregnant, nursing, or both. (I was both at the same time!) I had no idea it was controversial!

I tested positive for bacterial vaginosis at my 12 week check, when they did swabs for all sorts of things and drew blood. I guess different doctors make different decisions, but mine said that they always like to treat BV in pregnant women because of the risk of miscarriage and preterm labor.

I wasn't surprised to test positive, because I'd had it before. I had this horrible two-month cycle of yeast, BV, both at the same time, etc. It was awful! Finally cleared up. It was right after I went off birth control - guess my system was out of whack.

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